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You litterally cannot implement the C++11 memory model on early alphas without either

1) doing the equivalent of CAS (or LL/SC in this case) for every single access less than 32 bits completely destroying performance.

2) declaring that a char (and a byte) is 32 bit sized, which implies no posix.

It was very bad. This was fixed in subsequent alphas though.

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Interesting, TIL I learned that POSIX implies CHAR_BIT == 8.

I knew POSIX required a lot of other things that are unspecified in C/C++ but usually have a single sane implementation, but not that particular one. I know I have static_assert(CHAR_BIT == 8, ...) sprinkled around in quite a few places.

One day I'm going to write a header that just checks a big list of things that are "obviously sane" but not actually specified in C/C++, and error out if any are not true. Then I can include this in every project and just code in this new sane world. Not strictly portable, but "portable to where it matters".

With the C++ memory model you can make std::atomic<char> larger than char.

The issue is not with atomic but with all non atomic accesses. The standard guarantees that two concurrent writes to contiguous but distinct char-sized memory location to be legal and data-race-free.

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